The present invention relates to a structure of a wire cleaning guide to be used in wire bonding apparatuses and the like.
In semiconductor production processes, wire bonders are often used to provide connections between semiconductor dies and lead frames through metal wires. In such wire bonders, gold wires are used as connection wires. However, with the recent demand for faster and lower-cost semiconductors, metal wires other than gold, such as copper, are often used as connection wires due to its lower-cost but higher-speed signal processing performance.
The surface of metal wires such as copper is likely to be oxidized and covered with an oxide film if left in a high-temperature state or in the atmosphere for a long time. Such an oxide film causes a poor connection during wire bonding and results in a problem of deterioration in bonding quality.
Japanese Patent Application Unexamined Publication Disclosure No. 61-58246 discloses a technique for preventing heat induced surface oxidation by spraying inert gas onto a base metal wire such as copper between a wire feeder and a capillary as a bonding tool to prevent the surface of the base metal wire from being oxidized by the heating of the semiconductor dies and lead frames when using such wires for wire bonding.
Meanwhile, there has been employed a method for gold wires in which wires are coated with resin, for example, to prevent the occurrence of a short circuit between the wires after wire looping. However, in the case of using a coated wire for wire bonding, it is necessary to remove coating on the surface of the wire to expose its metal surface. As a technique for removing the coating on the surface of wires, there has been proposed a method, as disclosed in Japanese Patent Application Unexamined Publication Disclosure No. 5-211196, in which an induction coil is provided at the leading end of a bonding tool such as a capillary, and when grounding a wire on a lead frame using the bonding tool, a high-frequency current is applied to the induction coil to melt and remove the resin coating on the connection part of the wire, and then the wire is pressed and bonded to the lead frame by the bonding tool while operating an ultrasonic horn to generate a vibration.
There have also been proposed methods, as disclosed in Japanese Patent Application Unexamined Publication Disclosure No. 61-214530, in which resin coating is heated by a laser beam so that the resin on the connection part is melted and removed, and as disclosed in Japanese Patent No. 2723280, in which a wire coated with resin is inserted between discharging electrodes to heat, melt, and remove the resin coating by electrons emitted due to an electric discharge between the discharging electrodes.
Further, as for gold wires, it is often the case that a surface-active agent is applied onto the surface of wires to achieve higher-speed bonding operations. Such a surface-active agent is adapted to evaporate near the leading end of a bonding tool of a high temperature, causing a problem in that organic components contained are fixed firmly to the leading end of the bonding tool as contaminations and cause a gradual deterioration in bonding quality such as wire cutting behavior after a long time of use. It is therefore necessary to replace or clean the bonding tool at a predetermined time interval or after a predetermined number of times of bonding, creating a problem of reduction in bonding efficiency.
In wire bonding apparatuses is used a tensioner for applying a pull force to a wire that is inserted through a capillary as a bonding tool so that the wire does not sag. Japanese Patent Application Unexamined Publication Disclosure No. 2002-83837 discloses a tensioner in which the wire-spool side of a cylindrical nozzle holder is provided with a larger wire through hole than the capillary side, and compressed air supplied to the nozzle holder is discharged on either side so that a certain tension is applied to the wire by a fluid resistance that flows upward.
Japanese Patent Application Unexamined Publication Disclosure No. 2000-340599 also discloses a technique of cleaning electrodes on semiconductor chips by jetting gas that is transformed into plasma in a plasma generating section from the leading end gas ejection opening to the electrodes.
The conventional art disclosed in Japanese Patent Application Unexamined Publication Disclosure Nos. 5-211196 and 61-214530 and Japanese Patent No. 2723280 are methods for removing extraneous matters on the surface of wires. Although these conventional arts can remove resin coating on the surface of wires through a high-temperature heat treatment such as induction heating, laser heating, or discharge heating, the high-temperature treatment suffers from a problem in that the surface of the wires is oxidized and covered with an oxide film during the treatment. On the other hand, there is also a method of preventing wire oxidation by flowing inert gas in a discharge section as disclosed in Japanese Patent No. 2723280. However, there is a problem that it is difficult to remove oxide films formed on the surface of wires. In addition, the high-temperature treatment can cause the mechanical and/or electrical characteristics of wires to be changed, even if the oxide films can be removed, causing a problem in that the changes can cause poor connections and/or poor operation due to a reduction in adhesive performance. Further, in such a case of using a tensioner as disclosed in Japanese Patent Application Unexamined Publication Disclosure No. 2002-83837, the surface of wires at a high temperature is exposed to air containing oxygen to be further oxidized, creating a further a problem in that the problem of poor wire connections due to surface oxidation gets worse. Thus, the conventional arts disclosed in Japanese Patent Application Unexamined Publication Disclosure Nos. 5-211196 and 61-214530 and Japanese Patent No. 2723280 suffer from a problem in that foreign substances such as oxide films on the surface of wires cannot be removed effectively.
Although the conventional art disclosed in Japanese Patent Application Unexamined Publication Disclosure No. 61-58246 can prevent thermal oxidation just before bonding of copper wires on which surface oxidation has not yet occurred, oxide films that have already been formed on the surface cannot be removed. This always requires copper wires with no surface oxidation thereon to be used for bonding, causing a problem of limiting available wires. Also, if copper wires that have had oxide films formed on the surface thereof are used, the oxide films cannot be removed, creating a problem of deterioration in bonding quality such as a poor connection due to reduction in adhesive performance of the wires.
Also, for the same reason as above, the conventional arts disclosed in Japanese Patent Application Unexamined Publication Disclosure Nos. 61-58246, 5-211196 and 61-214530 and Japanese Patent No. 2723280 suffer from a problem in that surface-active agents applied onto the surface of gold wires cannot be removed effectively and/or easily.
Further, in such a conventional method of jetting plasma gas onto a to-be-cleaned body as disclosed in Japanese Patent Application Unexamined Publication Disclosure No. 2000-340599, the plasma gas is jetted from one side. Therefore, even if the method can be applied to wire cleaning, the entire circumference of the wire cannot be cleaned uniformly, suffering from a problem in that a poor connection can occur partially. Also, in such a method of blowing plasma gas against a wire, the jet changes the path as well as the tension of the wire, causing deterioration in bonding quality such as a poor connection.